Studies are being carried out with the aim of developing a method for controlling tumor growth by use of antiplasma cell antibodies which suppress blocking antibody formation and permit cytotoxic antibodies and sensitized lymphocytes to destroy the tumor. We shall also delineate the effect of antiplasma cell antibody on humoral antibody production and determine if differences can be distinguished between IgM and IgG plaque forming cells by means of particular antiplasma cell antibodies indicating that there are different classes of plasma cells with respect to surface antigens. Such differences would permit the preferential destruction of plasma cells producing blocking antibodies with destroying the cells producing cytotoxic antibodies. We shall determine whether antigenic differences which are other than those of the immunoglobulin antigen receptor can be found between plasma cells forming antibodies against different antigens showing that there is a heterogeneity of plasma cells corresponding to the specificity of antibody produced. We shall also determine the effect of antiplasma cell antibody on immunoglobulin levels in mice and the distribution between the different types of immunoglobulins. The above studies will be carried out with hetero and alloantisera against the plasma cell immunoglobulins. The studies will be carried out using antisera against mouse myeloma (plasma cell tumors) raised in rabbits and in allogeneic and syngeneic mice.